@Wouter: If this question isn't moved, then you should turn your "guess-comment" into a "fact-answer".
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KDNFeb 25 '13 at 19:06

This looks like physics to me, being focused on the device-level. Electronics.stackexchange.com seems more like circuit-level. Sorry for the misplacing though, if it is indeed misplaced. Thanks Wouter for the answer.
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arminski42Feb 25 '13 at 19:16

I wrote up an answer as @KDN suggested, since it's more clear than a comment.
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WouterFeb 25 '13 at 19:39

1 Answer
1

The $A/W$ units refer to the current (in Ampère) produced per Watt of light incident on the photodiode. This current-production happens when the diode operates in the so-called photoconductive mode. Since your question wasn't on the inner workings of a photodiode, I won't expand on this, but Wikipedia contains some more information if desired.